As in Hypersonic. It looks like the news has just been released about what's being touted as the follow-on to the SR-71 "Blackbird": the SR-72…name to be decided upon later apparently. Sparked by a cover story at Aviation Week, the news is popping up all over, as at the BBC, Defense Tech, WIRED, and elsewhere.
If nothing else, it appears Lockheed Martin has artwork ready - and a few more details at the company website. With the caption "Speed is the new Stealth", Lockheed Martin is summing up the principle virtue of this design. At Mach 6, it will be faster than any other air-breathing flying machine in the sky, at least twice as fast as the SR-71 Blackbird, now retired. There's nothing that can catch it - or so they expect.
The mission is straightforward as well: reconnaissance - flying cameras and other sensors over things we want to look at, when we want to look at them. This avoids the problem of waiting for a satellite with the right sensors to orbit overhead at a time when the weather will permit things to be 'seen'. Further, there's discussion of some kind of armaments as an option if some kind of strike is desired.
The technology is going to be game changing. Lockheed Martin is betting they can successfully build an aircraft around jet engines able to transition from turbines to pure ram jet and back.
The key to the new airplane, as it was with the SR-71, will be the engines. Lockheed Martin told Aviation Week the company has been working with Aerojet Rocketdyne to build an air breathing engine that combines both a traditional turbine and a scramjet to deliver the Mach 6 performance.(Aviation Week has a detailed set of graphics with the cover story.)
Normal turbine jet engines have problems operating at speeds beyond Mach 2. The original SR-71 used a complicated system of a movable nose cone on the engine, along with vents that prevented shockwaves from interfering with the flow, and slowed the air down enough so that it could be ingested by the engine. Though “unstarts” were a regular problem for Blackbird pilots, and caused problems throughout the life of the airplane.
The new SR-72 will use a turbine-based combined cycle (TBCC) that will employ the turbine engine at lower speeds, and use a scramjet at higher speeds. A scramjet engine is designed to operate at hypersonic velocities by compressing the air through a carefully designed inlet, but needs to be traveling supersonic before it is practical to begin with. So far research projects from NASA, the Air Force and other Pentagon entities have not been able to solve the problem of transitioning from the subsonic flight regime, through hypersonic flight with a single aircraft.
Further, they're betting they can build an airframe able to stand the high temperatures air friction will create, and with the range to make it worthwhile. And what's more it will be automated - a drone with no one on board. This actually makes some things simpler - keeping mere humans alive under the conditions this aircraft is intended to experience would add a lot of weight and complicated systems to the design.
The proposal is exciting, if only for the way it promises to advance the state of the art. BUT… even a prototype is several years away, and until hardware actually starts flying, there's no way to be sure Lockheed Martin will be able to make it work. They claim they have enough work done showing it is both practical AND affordable to begin work. There's a lot of experimental research into hypersonic aircraft, but to the best of my knowledge, actual flight time with working models is more commonly measured in minutes or even seconds - not the hours a working SR-72 will be expected to fly. Mach 6 is actually not as ambitious as some of the experimental programs have explored, so it's possible they're not kidding.
Further, costs are only estimates at this time. The real world usually ends up being a lot more expensive, if only because there are things you can only find out once you start trying to do this kind of thing for real. Future budget constraints or other programs could cannibalize this down the road.
And, the problem of operating an aircraft like this with no one on board poses special challenges. Lockheed Martin is talking about building a technology demonstrator that will have a pilot. I'm guessing the production aircraft is going to have to be much more autonomous than the sort of subsonic drones currently making up the bulk of the drone fleet. For one, there simply wouldn't be time for a pilot operating over a comm link to react to problems, not at the speeds the aircraft will be flying. (In fact, it's a question of whether or not any human would be able to fly this even if they were riding inside a cockpit without a lot of computer support to keep the aircraft "within the envelope.") For another, reliance on external signals (i.e.: command inputs from a remote operator, signals from navsats) are vulnerable to interference or even 'spoofing'.
Given how the SR-72 will be optimized for hypersonic speed, it's a bit much to expect it to be easy to fly at low speed for landing, and takeoff will be exciting. Lockheed Martin claims they've got the low speed end of the flight envelope within practical limits. Refueling it in flight - with no one on board - will not be a piece of cake either.
I'm speculating here, but it would make sense to me if the SR-72 ended up being carried aloft and launched in the air by a specialized larger plane. It wouldn't need to burn fuel to reach altitude, and it would make basing it a lot more flexible if the mothership could do the tedious work of flying the long routes needed to get it in position for a run. Recovering it afterwards would be… interesting to say the least. If it can be recovered in the air as well, it would not need to carry landing gear at all. And that's a fair amount of weight saved right there.
The Air Force has a lot of interest in this aircraft, if only because the technology needed to make it work will be essential for a proposed new manned bomber to enter service some point down the road in this century, because A) there will be no more new B-52s, B-1s, or B-2s - and B) their capabilities will no longer be match what the Air Force may need to do… whatever that may be.
(And before reflexive military bashing on spending can kick in, let me observe the Air Force will need something - because the current fleet will eventually wear out, and any kind of replacement is going to take years to develop, whatever it is. They always have to be thinking ahead - it's part of their job.)
I have several other things to offer for consideration on this. For one, the British seem to be pretty enthused about the SABRE engine, which also promises a revolution in aircraft design, one with a lot more potential than the Lockheed Martin proposal. An air-breathing rocket engine could make near space/LEO a lot easier to reach, and far more routine than at present. That too will be a game changer - and the British seem to be a lot farther ahead at the moment.
The X-37B program is another. A reusable robot spaceplane, it theoretically could be launched quickly, and could carry a variety of sensor packages for different missions. It can change its orbit, stay there for months, and land like an airplane. It's possible to see a fleet of these tasked with doing those critical reconn missions proposed for the SR-72, almost on-demand. They could not, however, launch any kind of strike from space - if only because of all the treaty problems this would cause.
Finally, there's one more thing that puzzles me. Why is all this SR-72 news taking place out in the open? Traditionally, these kinds of capabilities are developed in secret and kept secret for as long as possible. This news is giving the kind of 'targets' this aircraft might be used on a lot of lead time to start developing counter-measures. (Indeed, there are rumors the Air Force has already been operating a hypersonic aircraft in secret for some time now.)
Whatever happens, it will be some time before an SR-72 flies - if ever. Meanwhile, here's a BBC story on what it was like to fly the SR-71 - and another on the depressingly unlikely odds that a Concorde will ever fly again.
ADDENDUM: There's been some discussion in comments asking why we would need this aircraft when we have satellites. Well, as has been noted, it can take time before a satellite's orbit puts it in the right place at the right time and with the right weather to see something we badly want to see. The SR-72 could respond in hours, not days or weeks.
Further, there's another consideration. The kind of satellites that can give the clearest picture are in relatively low orbits - which means they are vulnerable to attacks that can take them out of action. (The Chinese have demonstrated this capability, for example.) If we rely primarily on satellites for critical information and other capabilities, they'd be the first targets of a serious offensive. We do not (as far as I know) have the capability to replace them with anything short of months or even years if they get knocked out. (Near-earth space orbitals would also become a lot less survivable for any satellites, with spreading orbital debris clouds. The movie Gravity makes this pretty clear, I understand.)
A hypersonic reconn aircraft would A) give us redundant surveillance capabilities that B) could be deployed more rapidly, and C) reduce the incentive to knock out satellites. Such an attack would in itself give pretty obvious indication that something was up - and with less to gain from it, it would be less useful for an adversary to attack in the first place.